fix: Support datetime with timezone and with millis

[Darkheir]

Description

Add support for datetimes without milliseconds or nanoseconds with a timezone set as it is supported by Elasticsearch.
The PR makes also date_optional_time and strict_date_optional_time_nanos more lenient with minutes and seconds as it was already the case for strict_date_optional_time.

How was this PR tested?

Unit tests

[rdettai-sk]

This is still not ISO 8601 compliant but definitively better. I also noticed that

• there doesn't seem to be a difference between yyyy-MM-dd['T'HH[:mm[:ss[.SSS][Z]]]] and yyyy-MM-dd['T'HH[:mm[:ss[.SSSSS][Z]]]]
• I think it should be strict_date_optional_time that forces yyyy-MM-dd and date_optional_time that has it optional

[Darkheir]

• I think it should be strict_date_optional_time that forces yyyy-MM-dd and date_optional_time that has it optional

It is complicated to find a good reference about the behavior inside Elasticsearch, but in their documentation it is written

Most of the below formats have a strict companion format, which means that year, month and day parts of the month must use respectively 4, 2 and 2 digits exactly, potentially prepending zeros. For instance a date like 5/11/1 would be considered invalid and would need to be rewritten to 2005/11/01 to be accepted by the date parser.

So there is nothing about the month and the days being mandatory or not...

I think that in both cases we should allow to have only the year or the year and the month.